The subject matter disclosed herein relates to determining the holding torque of a brake. More specifically, the subject matter disclosed herein relates to a method and apparatus for calibrating and testing the holding torque of a brake used in a material handling system.
Material handling systems are widely used, to lift heavy loads, weighing up to hundreds of tons. A typical material handling system includes at least one motor used to raise and lower the load and at least one additional motor to position the material handling system over the load to be moved. Common applications include manufacturing facilities, in which large components may be positioned for assembly and/or the final assembly may be moved for shipping. In the shipping industry, containers are loaded and unloaded between storage facilities, trucks, trains, and ships. Such material handling systems typically include a hook block, connected by a cable to a drum, which is, in turn, connected directly or indirectly through a gearbox, to the motor. The hook may be directly connected to a lifting point on the object or indirectly connected to the object via another lifting apparatus such as chains, slings, or custom structures. The motor then rotates in one direction to raise the load and in the other direction to lower the load.
During operation, a material handling system typically moves a load from a first location to a second location. The typical process for moving a load includes the following steps: positioning the material handling system over the load, lowering the hook to the load, securing the hook to the load, raising the hook and the load, moving the material handling system to the desired location, lowering the hook and the load, disconnecting the hook from the load, and raising the hook. During each step in the process, one or more axes of the material handling system may be involved. However, each axis is not involved in every step. Thus, to conserve energy and reduce wear on the motors a brake is typically set to prevent motion on an axis not actively being employed to move the load. In addition, the brake is typically rated to, apply a holding torque at some percentage greater than the rated torque of the motor. The extra holding torque is provided to ensure that the brake can hold the load or restrict undesired motion of the motor.
As is known to those skilled in the art, certain applications may require verification of the holding torque produced by the brake. For example, material handling systems used to move hazardous and/or very expensive loads may require such verification. Similarly, material handling systems used in applications where failure of a brake may result in danger to a human operator or another worker may also require such verification. Further, such verification must be performed not only upon commissioning of the system but on a periodic basis to verify continued safe operation of the brake. Thus, the holding torque must be determined in the field while installed on the material handling system and not just in the factory.
Existing methods for determining the holding torque of a brake have not been realized without certain drawbacks. For example, manual verification of the brake may be performed by attaching a torque wrench to a rotating member of the drive shaft. The torque wrench may be configured to supply the holding torque for the brake and a suitable force applied to the drive shaft via the torque wrench. However, this method of testing is limited in the amount of force a person may apply to the wrench or may alternately require a second mechanical device to apply the force to the wrench. Further, partial disassembly of the drive system may be required to manually perform the verification.
Alternately, a processor configured to coordinate operation of the brake and motor may generate a command to the motor to produce torque equal to the holding torque of the brake while leaving the brake set. However, this results in a pass/fail test of the holding torque of the brake and does not provide an indication of the actual holding torque provided by the brake. Thus, in the event the brake does not hold, an operator does not know how much adjustment of the brake is required.
Thus, it is desirable to provide a system configured to automatically determine the holding torque of the brake in a material handling system and provide an indication of the holding torque to an operator to facilitate calibration of the brake.